Power Supply

Hi All, I have been running my arduino like trinkets from an 18650 battery because it works and that's what my final project will be powered by. Since I am really becoming more and more interested and am already beginning another project I'm finding that a power supply may be handy. Something with enough power to do other cool things too would be nice. Short of buying a professional lab power supply I was wondering if something like these http://www.12volt-travel.com/12-volt-power-supplies-c-51_575.html would be okay if used with an LM317 voltage regulator to feed the arduino just 5v. This way I'd still have the full 12v available and plenty of current to play with as far as the arduino triggering external stuff.

Thanks, John

ehhh, I'm thinkin' ATX. Also, I'm thinking of turning one of these tiny trinkets and an oled into a 3 line volt meter. I think it would be a super cool project. On top of that I already own the atx power supply and they put out a ton of amps!

EDIT** funny, we were posting at the same time. =0)

bumba000:
Hi All,
I have been running my arduino like trinkets from an 18650 battery because it works and that’s what my final project will be powered by. Since I am really becoming more and more interested and am already beginning another project I’m finding that a power supply may be handy. Something with enough power to do other cool things too would be nice. Short of buying a professional lab power supply I was wondering if something like these http://www.12volt-travel.com/12-volt-power-supplies-c-51_575.html would be okay if used with an LM317 voltage regulator to feed the arduino just 5v. This way I’d still have the full 12v available and plenty of current to play with as far as the arduino triggering external stuff.

Thanks, John

Why an LM317 if you want 5V output? LM317’s are fine for voltages not covered by the standard regulators, but overkill otherwise.
A plain old LM7805 is all you need for 5V, or even an LM78L05 or LP2950-5 for <100mA.

And just how much power do you plan to need at 12V? What sort of projects? An ATX supply as you mention in your next post might well be overkill, or the voltage might not be suited to your future projects.
I just use 12V regulated 0.5A to 2A plug-packs or a 12V 7Ah SLA battery & an LM7905 for prototyping, and find them more than suitable for 90% of my projects. Then with the final version, I buy or build the right power supply to suit the specific application.

..well Steve, I was going with LM317 because that's all I know knew about. You have just expanded my horizons. I thank you for that.

I have made a lab power supply from an ATX power supply. It's great! It looks like shit, but it's great. Trouble is I thought I had plenty of banana jacks. I reality I had just two. So I went ahead and drilled the required holes and then went to buy more banana jacks - they had only small jacks. So I had to make the holes smaller using washers and a mig welder. :slightly_frowning_face:

I did have a rocker that fit perfectly into the hole where the wires used to be, so that worked out pretty well.

12v ~ 7.5a, 5.5v ~ 14a, 3.3v ~ 19a. Perfect!

|500x281

bumba000:
…well Steve, I was going with LM317 because that’s all I know knew about. You have just expanded my horizons. I thank you for that.

I have made a lab power supply from an ATX power supply. It’s great! It looks like shit, but it’s great. Trouble is I thought I had plenty of banana jacks. I reality I had just two. So I went ahead and drilled the required holes and then went to buy more banana jacks - they had only small jacks. So I had to make the holes smaller using washers and a mig welder. :slightly_frowning_face:

I did have a rocker that fit perfectly into the hole where the wires used to be, so that worked out pretty well.

12v ~ 7.5a, 5.5v ~ 14a, 3.3v ~ 19a. Perfect!

That looks good to me John. Sort of space-age. :wink:
As mentioned, the big limitation is that it only has a maximum of 12V, but if that’s all you’ll need, all is well. :slight_smile:

My bench-top power supply, (which I rarely use because it takes up too much table space), was made using the switching power supply from a large, commercial printer that also had a computer motherboard. Luckily, though, it also had a 32V rail for the print-heads, so I used a separate internal regulator to get an adjustable supply from 1.25V to about 30V, along with the +5V, +12V and -12V rails. Not as high-powered as your’s, but I can draw 4A from the adjustable 1.25-30V rail, 1.5A from the -12V rail, 1A from the +12V rail and 8A from the 5V. It’s worked faithfully for over 20 years now. Like your’s there’s a fan in the original PSU - it blows out the back of my box and has an input vent on the side.
(Pic attached.)

The printer was a good example of governments throwing money away. I bought it brand new as surplus. The government bought 2000 of these printers, to print postage stamps, receipts, scan documents and a few other functions. They were to be installed in post-offices.
They even had half a dozen large, high-quality Minebea bi-polar stepper motors in them.

No sooner did they get them made than they changed their mind and sold them off as surplus. I’m not sure just how much the government originally sold them for, but I got mine, (3 in total), for $41 each. The printers would have cost a couple of thousand dollars each to get made back then. I still have a number of the stepper motors here. They were the reason I bought the printers in the first place. The PSUs were a bonus, along with many other useful bits and pieces. (Photo-interruptors, microswitches and other sensors in particular.)
They were a fantastic score. :slight_smile:

Power Supply.JPG

Nice score SteveO! Wow, I'm looking at two printers right now that could turn into a pile of really cool parts. Governments are crazy. They think money grows on trees I guess. Well I've some learning to do myself.

Just thinking on the subject of stepper motors - you'd need a stepper controller which you'd have inside of a printer. Well then you'd need a way to speak to the controller. How would ya do that? To think - if I could answer that question just how many awesome things I could have made from all of the printers that I've tossed out.

bumba000: Nice score SteveO! Wow, I'm looking at two printers right now that could turn into a pile of really cool parts. Governments are crazy. They think money grows on trees I guess. Well I've some learning to do myself.

Just thinking on the subject of stepper motors - you'd need a stepper controller which you'd have inside of a printer. Well then you'd need a way to speak to the controller. How would ya do that? To think - if I could answer that question just how many awesome things I could have made from all of the printers that I've tossed out.

Actually, the stepper driver ICs in the printers were surface-mount, so couldn't be re-used. I have a number of various stepper driver chips that I regularly use, though, so that wasn't an issue. I'm new to Arduinos, but have been using PIC micros for 20 years plus, as far as a controller is concerned.

An Arduino is the perfect thing for controlling stepper motors, and rather than just buying driver ICs, there are a range of very cheap stepper driver modules on the internet that make it really easy, especially using the Arduino stepper library. I have L298s and L6208s here now, but bought a stepper driver board on the internet the other day for only AU$4.99 delivered. It's based on an L298N. This is it:- 1 pc L298N RED Dual Stepper Motor Driver Controller Board Module

Those printers of your's could have some nice stepper motors in them. :)

My bench power supply is a converted ATX power supply. It exposes +/- 12V, +/- 5V and +3.3V. It also has a LM317T on it for variable voltage with a digital voltmeter included. This LM317T is powered from GND and +12V.

I am, however, making two changes to it:

a) adding a LM337: a negative voltage regulator, up to 1.5A. It is the "negative version" of the LM317. I find that it is quite useful to have variable negative voltages too, specially if you're working with op amps and sound signals, which do have negative voltages. It will be powered from the -12V rail.

b) adding an ammeter (current meter) do the variable part of the PSU.

c) Replacing the LM317 (1.5A) for a LM338 (5A), with a proper heatsink.

Here's what it looks like (before the changes above): |500x462

AlxDroidDev: My bench power supply is a converted ATX power supply. It exposes +/- 12V, +/- 5V and +3.3V. It also has a LM317T on it for variable voltage with a digital voltmeter included. This LM317T is powered from GND and +12V.

I am, however, making two changes to it:

a) adding a LM337: a negative voltage regulator, up to 1.5A. It is the "negative version" of the LM317. I find that it is quite useful to have variable negative voltages too, specially if you're working with op amps and sound signals, which do have negative voltages. It will be powered from the -12V rail.

b) adding an ammeter (current meter) do the variable part of the PSU.

c) Replacing the LM317 (1.5A) for a LM338 (5A), with a proper heatsink.

So we're not the only ones to re-purpose this sort of PSU. :) I like the idea of having a variable -ve supply as well. Good for dual supply op-amps. And I envy your digital volts display. I should have put in a digital one myself, more accurate and easier to read, but at the time I had the moving-coil meter just sitting there and didn't have a digital meter on hand.

For years I've been meaning to add variable current-limiting, too, but never get around to it. :(

OldSteve: So we're not the only ones to re-purpose this sort of PSU. :)

It is quite common, actually.

That big silver knob on the variable section of my PSU is a switch potentiometer (2K, linear). That means it can turn the entire LM317T, green led and voltmeter ON and OFF. This way I don't have to waste power on the LM317 if I am not using it.

The voltmeter is powered by the +5V rail on the PSU. There is also a 5W 10 Ohm resistor inside the PSU, permanently connected to the +5V rail, so there is some load on the PSU at all times. This prevents it from "hissing".

I also changed the cheap 8cm fan for a thinner, more efficient and more silent one.

Another option I am studying to have negative voltage on my PSU is to use a TL7660: it'll be much simpler to implement than a LM337 (which may require an additional potentiometer or replacement of the one I have for a double one).

AlxDroidDev: It is quite common, actually.

That big silver knob on the variable section of my PSU is a switch potentiometer (2K, linear). That means it can turn the entire LM317T, green led and voltmeter ON and OFF. This way I don't have to waste power on the LM317 if I am not using it.

The voltmeter is powered by the +5V rail on the PSU. There is also a 5W 10 Ohm resistor inside the PSU, permanently connected to the +5V rail, so there is some load on the PSU at all times. This prevents it from "hissing".

I also changed the cheap 8cm fan for a thinner, more efficient and more silent one.

Another option I am studying to have negative voltage on my PSU is to use a TL7660: it'll be much simpler to implement than a LM337 (which may require an additional potentiometer or replacement of the one I have for a double one).

That's a good idea having a separate switch on the variable supply, although not much of a power saving since having the display power connected to the 5V rail means that when not in use, the LM317 will only draw bias current plus the current through the 'adjust' voltage divider. Despite that, it's good being able to isolate the variable supply anyway.

I considered also adding a diode network to allow my 317T to go right down to 0V, but load regulation suffers a bit doing that, so I stayed with the 1.25V minimum. After all, lower voltages are rarely needed, and if they are more often than not a voltage divider will suffice.

Still, despite having the power supply sitting here, usually I just use the 12V 7Ah SLA battery to power my test circuits, because it takes up almost no bench (kitchen table) space. (And an LM7805 takes very little space on a breadboard.)

bumba000: So I went ahead and drilled the required holes and then went to buy more banana jacks - they had only small jacks. So I had to make the holes smaller using washers and a MIG welder.

Enterprising - and it looks the part.

I (or my father when he was alive) would have nibbled the panel out and screwed/ pop-riveted a fresh panel over.

OldSteve: Actually, the stepper driver ICs in the printers were surface-mount, so couldn't be re-used.

Hacksaw.

AlxDroidDev: That big silver knob on the variable section of my PSU is a switch potentiometer (2K, linear). That means it can turn the entire LM317T, green led and voltmeter ON and OFF. This way I don't have to waste power on the LM317 if I am not using it.

Compared to the the power drawn by a running (or idling) ATX power supply that sounds a trifle absurd to me. :astonished:

Paul__B: Hacksaw.

When I said "Actually, the stepper driver ICs in the printers were surface-mount, so couldn't be re-used.", I really meant, (and should have said), that it just wasn't worth the effort. :D (Especially since I hate working with SMD parts.)